Ion-selective electrodes in organic analysis: Determination of carboxylic acids via in situ conversion into amines

An ion-selective electrode system has been developed for the determination of carboxylic acids via in situ conversion into amines, The Schmidt reaction was applied to convert carboxylic acids into their corresponding amines. The amines were then determined by an ion-selective electrode based on a calix[6]arene hexaester ionophore. The electrode exhibited a Nernstian slope of 58.5 mV per concentration decade and a detection limit of 2.8 x 10(-5) mol l(-1) for the determination of nonanoic acid. The effect of the length of the carbon chain in carboxylic acids on the response of the electrode was also studied, A stronger response was observed for the carboxylic acids with a carbon number greater than 8. The detection limit for the determination of dodecanoic acid was 7.1 x 10(-7) mol l(-1).